Article Text

Environmental and dietary interventions in the first 5 years of life did not reduce risk of asthma and allergic disease
  1. Thomas M Ball, MD, MPH
  1. University of Arizona, Tucson, Arizona, USA

    Statistics from

 Q Does reduction in exposure to house dust mite (HDM) allergens and modification of dietary fatty acids in the first 5 years of life reduce the risk of asthma at 5 years of age?

    Clinical impact ratings GP/FP/Primary care ★★★★★★☆ Allergy & immunology ★★★★★★☆ Paediatrics ★★★★★☆☆


    Embedded ImageDesign:

    randomised, 2×2 factorial design, placebo controlled trial.

    Embedded ImageAllocation:


    Embedded ImageBlinding:

    blinded {participants [diet intervention only], outcome assessors, and laboratory staff}.*

    Embedded ImageFollow up period:

    5 years.

    Embedded ImageSetting:

    {antenatal clinics of 6 hospitals in Sydney, Australia.}

    Embedded ImageParticipants:

    616 pregnant women (mean age 29 y), whose unborn singleton child was at increased risk of developing asthma because of asthma or frequent wheezing in a first degree relative. Exclusion criteria included a cat in the home and a vegetarian diet. Infants born at <36 weeks’ gestation, with birth weight <2.5 kg or significant congenital malformation or neonatal disease were withdrawn.

    Embedded ImageInterventions:

    active HDM intervention (n = 308), consisting of an allergen impermeable barrier on the child’s bed and pillow, regular washing of bedding, and use of a benzyl benzoate containing solution in the wash every 3 months; or control HDM (n = 308), consisting of usual care. Active diet intervention (n = 312), consisting of canola-based oils and spreads for food preparation and tuna oil capsules (added once daily to formula or to solid foods from 6 mo of age) to increase the ratio of ω-3 to ω-6 fatty acids; or control diet (n = 304), consisting of polyunsaturated oils and spreads and Sunola oil capsules.

    Embedded ImageOutcomes:

    probable current asthma; wheeze pattern (frequency and duration of episodes) and time course (early or late onset, transient or persistent); cough without cold; rhinitis; eczema; atopy (positive skin prick tests); and spirometric function.

    Embedded ImageParticipant follow up:

    84% {intention to treat analysis}.


    Neither HDM avoidance nor dietary fatty acid modification reduced the risk of asthma, cough without cold, rhinitis, or eczema more than control (table). Neither intervention affected the pattern or time course of wheeze, the prevalence of atopy, or the level of lung function.

    Interventions in the first 5 years of life to prevent asthma and allergic disease at 5 years of age*


    Reduction in exposure to house dust mite allergens and modification of dietary fatty acids in the first 5 years of life did not reduce the risk of asthma or allergic disease at 5 years of age in children at high risk.


    Although the Childhood Asthma Prevention Study by Marks et al was successful in decreasing levels of HDM allergen in the environment and increasing the ratio of ω-3 to ω-6 fatty acids in the plasma of the children, no significant differences in clinical outcomes between treatment and control groups were found at 5 years of age. This lack of efficacy of allergen avoidance in the primary prevention of asthma corroborates the negative results of previous studies.1 Supplementation with ω-3 fatty acids is safe during pregnancy and infancy and seemed promising in previous observational studies.2 While the lack of efficacy found in the study by Marks et al is disappointing, we should await results of other randomised trials before drawing more definite conclusions.

    A common challenge to prevention trials for asthma is that, in general, wheezing in the first few years of life is primarily of infectious origin, while later wheezing tends to reflect allergic asthma. Therefore, interventions targeting atopy, such as those performed in this study, probably require assessment of asthma after 5 years of age. It is also possible that future interventions will need to be tailored to the specific genetic makeup of the individual mother and infant.1

    In the interim, what can we recommend to concerned parents? Firstly, avoid prenatal tobacco exposure during fetal lung development. Secondly, although not without debate, encourage breast milk or partially hydrolysed infant formula for high risk infants. Thirdly, parents may consider maternal exclusion diets or use of probiotics in hopes of preventing atopy. Lastly, allergen avoidance is only helpful for the sensitised child,3 not for primary prevention, and let’s hold our breath awaiting more results regarding ω-3 fatty acids.


    View Abstract


    • * See glossary.

    • For correspondence: Dr G B Marks, Woolcock Institute of Medical Research, Camperdown, New South Wales, Australia. g.marks{at}

    • Sources of funding: National Health and Medical Research Council of Australia and New South Wales Department of Health.

    Request permissions

    If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.

    Linked Articles

    • Glossary
      BMJ Publishing Group Ltd
    • Other articles noted
      BMJ Publishing Group Ltd